雅鲁藏布江古洪水事件和历史径流序列重构

This study aims to reconstruct the paleoflood events and decadal streamflow series since the early Holocene for the Yarlung Tsangpo River and to support the planning and design of hydro projects in this river basin. In the 10,000-year time scale, the Yarlung Tsangpo is a young and active river on the Tibet Plateau. Climate change (e.g., precipitation and temperature variation) has resulted in glacier advance and retreat, streamflow variation. Tectonic uplift and colluvial and fluvial processes have caused active adjustment of river morphology. Monsoon rainstorms and barrier/glacier lake outbursts have triggered floods with different patterns. Eventually, information of flood events and streamflow variation recorded by sediment deposits in river terraces and lakes were disturbed by these complex coupled processes. Therefore, this study focuses on three hypotheses: sedimentary records from multiple sources facilitate the reconstruction of paleoflood events; sedimentary sequences in lakes correspond to the series of streamflow; and fluvial features of the canyons reveal the historical channel evolution. Using integrated approaches of paleohydrology, limnology, fluvial geomorphology and hydraulics, this study will provide reconstructed data sets of paleoflood events and streamflow series in the Holocene, clarify the dominant mechanisms and factors influencing the flow series, and provide new approaches for paleohydrologic reconstruction. This study has important scientific significance in terms of supporting or clarifying climate change, revealing runoff variation and river evolution patterns in the areas subject to active tectonic movement. It will also be conducive to enhance the ability of forecasting flood and streamflow change in the Yarlung Tsangpo River.

本项目以重构雅鲁藏布江万年以来古洪水事件和径流序列、支撑水利水电工程规划设计为目标导向。在万年时间尺度上，雅鲁藏布江是一条年轻的高原河流：降水、气温等气候波动导致了径流变化，构造抬升、塌积过程与冲积过程使河道快速调整，暴雨/冰雪融水、堰塞湖溃决塑造了不同洪水类型。洪水沉积物、湖泊沉积物、河流形貌等记录的历史径流与古洪水的信息受这些复杂过程的干扰。本项目针对“古洪水事件重建的多源沉积证据链”、“湖泊多指标沉积序列与径流序列的定量关系”、“峡谷河段的洪水造床特征”等三个科学问题，通过古洪水水文学、湖泊学和水沙动力学、河床演变学等交叉，获取雅鲁藏布江全新世以来的古洪水与径流变化序列数据、揭示古洪水和径流变化机制及其主控因素，提出重构古洪水和径流变化的新方法。本研究将有助于佐证或阐释万年以来的气候变化、径流演变规律与强构造运动区的河流演变模式，提升对雅鲁藏布江未来洪水事件和径流变化的预测能力。

本项目以重构雅鲁藏布江万年以来古洪水事件和径流序列为目标，聚焦古洪水事件重建的多源沉积证据链、湖泊多指标沉积序列与径流序列的定量关系、峡谷河段的洪水造床特征三个科学问题。通过四年研究，完成项目研究任务，取得如下新进展：.（1）针对雅江中上游典型湖泊，通过湖泊沉积岩芯采样与多指标分析，重建了过去1.8和2.1万年以来独立的径流、洪水变化记录（分辨率2年）和过去万年以来的降水、气温信息（分辨率115年）。模拟生成雅江干流古径流序列，分析气候、径流数据的周期性和变化趋势，检验径流和降水的突变点，揭示了雅江干流径流变化趋势、古洪水事件时间分布特征的空间差异。.（2）考虑不同基岩抬升速率，计算分析16 ka以来雅江峡谷河道在周期性堰塞-溃决事件作用下的演变过程。在抬升速率1.6 mm/年和堰塞坝高100 m、周期100年的典型情景下，受泥沙冲淤和基岩抬升共同作用，2 ka、7 ka、11 ka至今可分别形成最大3.0 m、8.5 m、10.9 m的河床净抬升；相对于隆升控制的河岸，河床下切达0.2 m、2.7 m、6.7 m。.（3）在雅江干支流发现大型沉积边滩、滞流洪水沉积物、湖相沉积物等沉积证据。根据沉积物年代框架和空间水力学联系，重建了雅江干流和易贡藏布江3次高能古洪水事件和5期古洪水事件。由于高能古洪水沉积物拔河高度一般超过百米，河床下切对古洪水洪峰流量估算结果影响不大。.（4）探讨了全新世以来气候快速显著变化-大型滑坡事件对雅江古溃决洪水事件和径流的影响，表明径流变化受印度季风和冰融水的共同作用、洪水受厄尔尼诺-南方涛动（ENSO）的影响。.项目完成学术论文38篇，其中SCI论文24篇、EI论文5篇、国内核心期刊9篇，培养博士11名，授权发明专利2项、软件著作权1项。项目负责人获第十四届钱宁泥沙科学奖，1名研究骨干获得国家杰出青年科学基金资助，向国家提出并被采纳咨询建议2项。